Application of interlaminar shear strength and finite element modeling for failure analysis of 3D printed continuous fiber-reinforced composites

Continuous fiber-reinforced plastic composite materials are being increasingly used in material extrusion additive manufacturing, typically fused filament fabrication, because it enables unprecedented freedom to manufacture high-performance parts on demand and on-site. Interlayer weaknesses of continuous fiber-reinforced plastic composites made by additive manufacturing need to be addressed to assure the structural integrity of a design that is inherently anisotropic, commonly determined by characterization of interlaminar shear strength. In this study, interlaminar shear strength of 3D-printed continuous fiber-reinforced plastic composites was characterized with a single-lap joint specimen. It was observed that the interlaminar shear strength and failure mode changes as a function of the fiber orientation. The layup sequences were found to affect the stress distribution over the joint area, causing non-tensile failure regarding the eccentric load. The bonding quality data were compared to finite element analysis results to map the effective load transfer to the interlaminar area between each printed laminated structure. Stress distribution of the 3D-printed laminated structure under tension loading can be complex, and the results from such tests can be misinterpreted. Based on the present investigation, it is recommended that the layup design should incorporate a balanced stiffness to take advantage of continuous fiber reinforcement.